At what point does tight letter-spacing stop looking refined and start hurting legibility?

Tightening letter-spacing crosses from refined into harmful at the point where letters begin to touch, merge, or blur at the size they are read, and that point depends almost entirely on size rather than on a single tracking value. On large display type, pulling the letters slightly closer can look polished and intentional, because at big sizes the default spacing often looks loose and a small negative adjustment tightens the word into a unit. At reading sizes the same instinct backfires, since body text needs every bit of its built-in spacing to keep individual letters distinct. Legibility, not aesthetics, sets the floor.

The reason size governs the threshold is that letter-spacing scales with the type but the eye’s need for letter separation does not. A typeface’s designer already set its default spacing to read well at text sizes, so that default is a deliberate optimum, not a starting suggestion to improve on. When type is enormous, the gaps between letters look proportionally large and a touch of negative tracking restores a tighter, more deliberate texture. When type is small, those same gaps are already near the minimum the eye can use to parse one letter from the next, so removing any of them pushes adjacent shapes into each other and the reader’s recognition of word shapes degrades. The mechanics of recognizing a word depend on seeing its letters as separate forms, and tight tracking attacks exactly that.

A concrete version designers will recognize: a hero headline set at sixty pixels can take maybe a small negative tracking and look crisp and confident, the words reading as solid blocks rather than spaced-out strings. The same designer, wanting the body copy to share that confident look, applies negative tracking to a sixteen-pixel paragraph. Now the “r” and “n” start to look like an “m,” the “cl” reads as a “d,” and the reader slows down without consciously knowing why, because the letterforms are colliding at the scale where collisions actually obscure meaning. The headline was helped; the paragraph was sabotaged. The fix is to leave body tracking at or very near the font’s default and reserve negative tracking for display sizes alone.

The nuance worth naming is that this is a spectrum, not a switch, and a few cases sit between the poles. All-caps settings, even at smaller sizes, often benefit from a little positive tracking, since capitals were designed to sit in the flow of lowercase and look cramped when run together as a label. Some text faces at small sizes actually read better with a hair of positive tracking on dark backgrounds, where light type blooms. And the safe display tightening is modest; pulled too far even a giant headline turns into a smear. The rule is directional: as size goes up, a little tightening can refine; as size comes down toward reading, hands off.

So tie your tracking decisions to size. Tighten only large display type, and even then by a small amount checked against the actual rendered word rather than a number you trust on faith, and leave body and other reading-size text at its default spacing, nudging caps and labels slightly looser if anything. When in doubt, set the text at its real size and ask whether any two letters are starting to touch; the moment they do, you have passed the line and should back off.